This invention relates to electrical supply line protection apparatus. It has application in the protection of three terminal lines (Teed circuits).
Three terminal lines, or Teed circuits, often offer considerable economic, technical and environmental advantage over 2-terminal lines. However, it is well known that, for a number of reasons such lines are often considerably more difficult to protect than plain feeders using conventional unit or non-unit protection techniques. Of the alternatives, differential protection is generally regarded as the method which is fundamentally best suited to Teed feeders, but it is only recently that communication channels have become available that are capable of transmitting both phase and amplitude information with a sufficiently large dynamic range and over a distance compatible with requirements of the transmission line protection.